1. Field of the Invention
This invention relates to a magnetic head for use with a magnetic disk storage apparatus, and more particularly to a magnetic head slider for a magnetic head and a production method therefor.
2. Description of the Related Art
The recording density of a magnetic disk storage apparatus has exhibited a significant augmentation in recent years. Particularly, the technique of reducing magnetic spacing between a magnetic head element and a magnetic recording medium, which augments the track recording density, has exhibited a progress, and a magnetic disk apparatus which incorporates a magnetic head of a very low flying type whose flying height is 30 nm or less has been put into practical use.
However, while such reduction in flying of a magnetic head brings an increase of the track recording density, an apparatus of a so-called contact start stop system hereinafter referred to as CSS system which is employed widely in hard disk apparatus and wherein starting and stopping are performed while the magnetic head remains in contact with the magnetic disk has a problem in that, if a magnetic disk surface is formed very smooth as a mirror surface and the magnetic head is left in close contact with each other for a long time, then the magnetic head tends to stick to the magnetic disk surface. The head sticking degrades the mechanical durability and the reliability of the magnetic disk apparatus.
One solution for this problem is to provide a protective film on an air bearing surface of a magnetic head slider. For example, it is disclosed in Japanese Patent Laid-open No. 63-2-8912, November 1988 to fluoridate an air bearing surface of a magnetic head slider made of glassy carbon to produce a graphite fluoride layer so that the wear of the magnetic recording medium is suppressed and a starting failure or a stick slip phenomenon which arises from the head sticking to the medium is prevented by a good solid lubrication characteristic of the graphite fluoride layer.
Further, in expectation of a similar effect, a magnetic head has been put into practical use wherein a carbon film is provided on an air bearing surface of a slider by a chemical vapor deposition (CVD) method or a sputtering method.
Meanwhile, in order to prevent sticking between the surface of a magnetic disk medium and a slider when a magnetic disk apparatus is inoperative, an air bearing surface of the magnetic head slider is formed convex called crown. The convex forming work is usually performed by mechanical polishing such as lapping as disclosed, for example, in Japanese Patent Laid-Open No. 4-358378, December, 1992.
Also the following methods have been proposed for the crown forming other than mechanical polishing.
1) A method wherein a groove is provided at a portion on the opposite side of an air bearing surface by mechanical working and a crown shape is formed making use of a difference in working distortion arising from the position, the shape, the dimension or some other factor of the groove as disclosed, for example, in Japanese Patent Laid-Open No. 1-267822, October, 1989 or another method wherein a crown is formed making use of a difference in coefficient of thermal expansion between an organic resin filled in a groove and a slider material as disclosed in Japanese Patent Laid-Open No. 62-6475, January, 1987.
2) A method wherein a piezoelectric element is securely mounted on a rear surface to an air bearing surface of a slider and a voltage is applied to the piezoelectric element to deform the slider to form a crown as disclosed in Japanese Patent Laid-Open No. 1-166382, June, 1989 and so forth.
3) A method wherein a protective thin film is provided on an air bearing surface of a slider and the film thickness of the slider protective film is varied continuously such that a central portion of a slide rail in a longitudinal direction may project by a predetermined extent to shape the air bearing surface into a crown shape.
However, the magnetic head slider protective film has the following problems.
In order to reduce the magnetic spacing for increasing the magnetic recording density, the slider protective film is preferably formed as thin as possible, but in order to assure the mechanical durability, it is effective to form the protective film as thick as possible. In this manner, in the slider protective film, the two factors for increasing the recording density and the assurance of the durability have a trade-off relationship to each other. Accordingly, in order to solve this relationship, the protective film should be formed with such thickness that it has a comparatively great thickness in the region of the air bearing surface which contacts with and slides on the magnetic disk surface with a high probability and creates a factor which defines the mechanical durability, but has a comparatively small thickness in the region of the magnetic head element which creates a factor which defines the recording density.
As a solution for this problem, a method is disclosed in Japanese Patent Laid-Open No. 7-65527 mentioned hereinabove wherein a protective film is provided on an air bearing surface of a slider and, upon formation of the protective film, the film thickness is controlled to vary continuously by opening/closing of a shutter to form a crown shape on the air bearing surface.
However, the last-described method still has some problems as follows.
Generally, since a carbon type thin film used for a slider protective film has a coefficient of static friction with the surface of a magnetic disk, the probability that the slider may stick to the disk surface to put the magnetic disk apparatus into a starting disabled condition is high. Further, a protective film of the carbon type provided on a magnetic head slider requires a crown amount larger than that of another magnetic head slider without a protective film. Further, where the film thickness of a protective film is controlled by opening/closing of a shutter upon film formation, there is a problem in controllability in film thickness or mass productivity.
Further, where a crown shape is formed on the full area of an air bearing surface, the crown shape is restricted in order to minimize the flying height of a magnetic head element. For example, the crown amount is limited such that, with a slider of 50% or called "nano" (2 mm long.times.1.6 mm wide.times.0.5 mm high), a central portion of the air bearing surface remains within the range of 30 to 50 nm from the opposite ends of the air bearing surface, and with another slider of 30% or called "pico" (1.2 mm long.times.1 mm wide.times.0.3 mm high), a central portion of the air bearing surface remains within the range of 10 to 30 nm from the opposite ends of the air bearing surface. Besides, since not only this crown amount is insufficient for reduction of sticking but also the film thickness of the protective film is limited to this thickness, it is difficult to improve the durability.
Further, the problem when producing a crown by mechanical polishing or grooving resides in the shape itself and the working accuracy of the crown. In particular, since the working shape is limited, forming a crown of a complicated shape, wherein a convex shape is formed partially in an air bearing surface while the other part is formed flat, is impossible as far as it relies upon mechanical polishing or grooving.
Furthermore, if the desired crown height is set, for example, to 30 nm, then the standard deviation of the crown height by conventional mechanical polishing is 7 to 8 nm. On the other hand, a remarkable increase in recording density of a magnetic disk apparatus in recent years strongly requires smoothing of the surface of a magnetic disk and reduction of the flying height of a magnetic head slider. However, as the smoothness of the magnetic disk surfaces increases, the magnetic head slider increases its sticking to the disk surface. In other words, the coefficient of static friction between the magnetic head slider and the magnetic disk surface tends to increase. Therefore, for the crown amount which is an important factor which dominates sticking, a working accuracy of a higher level than ever, that is, the standard deviation of less than 2 nm for the average crown height of 30 nm, is required. Accordingly, in the present situation, this working accuracy cannot be satisfied with the crown working method which is based on mechanical polishing or grooving.
Meanwhile, the method of applying a voltage to a piezoelectric element securely mounted on a rear surface of a slider to form a crown is disadvantageous in terms of the production cost or the productivity since fixed mounting of the piezoelectric element and a voltage driving and controlling circuit are required separately.